In the production of U- or V-section channel bars or of T-section bars the bar widths normally vary from bar to bar within a range, lying between a minimum bar width and a maximum bar width. In order to form a stack of such bars a succession of the bars is fed to a pickup station with the bars generally coplanar, parallel, and in edge contact in the pickup station. At this station a pickup device, normally formed by an electromagnet assembly, picks up a predetermined number of the bars and deposits them in a stacking station.
The principal disadvantage of this system is that if the group of bars picked up contains a plurality of bars having the minimum bar width, it is possible for the group to have too many bars, or similarly if a few of the bars are relatively wide the group picked up can number one bar too few. The obvious result is that the stack thus formed will have an incorrect number of bars.
This above-discussed problem is compounded when the bars are of the channel type, that is of U section, V section, or C section. With such bars it is normally necessary to invert every other layer of bars in the stack, with the alternate layers each numbering one less bar than the layers sandwiching it. In such a stack, if a given layer has one bar too few or too many, the result will be an incorrectly constituted stack that will normally require complete manual restacking.
Another disadvantage of the known system is that if the bars overlap each other occasionally as they are picked up, when deposited the bars are irregularly positioned in the layers of the stack. The result of this is, of course, that the layers will not lie flatly or neatly on top of each other, and that it will be impossible to form a neat planar layer on top of such an irregularly constituted layer.
Another disadvantage of this machine is that the electromagnets normally employed to hold the bars, when same are magnetically attractable, are bulky and very heavy, and at the same time require considerable energy to use. Thus the known stacking machines not only are expensive to make and operate, but at the same time function imperfectly.